import CoreLocation
import CoreMotion
import Foundation
import Observation
import SceneKit

// MARK: - SunseekerViewModel

/// Owns all sensor state for the Sunseeker AR overlay.
/// Separates CoreLocation / CoreMotion concerns from the ARKit view layer.
@Observable
final class SunseekerViewModel: NSObject, CLLocationManagerDelegate {

    // MARK: - Published State

    /// True once we have both a GPS fix and a valid heading.
    private(set) var isReady  = false

    /// Latest GPS coordinate. nil until first fix.
    private(set) var coordinate: CLLocationCoordinate2D?

    /// Latest true heading (0 = North, clockwise).
    private(set) var heading: Double = 0

    /// Dense hourly arc for today.
    private(set) var arc: [(date: Date, position: SunPosition)] = []

    /// Current real-time sun position (updated every second).
    private(set) var currentPosition: SunPosition?

    /// Sunrise and sunset for today.
    private(set) var riseSet: (rise: Date?, set: Date?) = (nil, nil)

    /// Diagnostic string for the UI when location access is denied.
    private(set) var locationError: String?

    // MARK: - Private

    private let locationManager = CLLocationManager()
    private let motionManager   = CMMotionManager()
    private var updateTimer: Timer?

    // MARK: - Init / Deinit

    override init() {
        super.init()
        locationManager.delegate          = self
        locationManager.desiredAccuracy   = kCLLocationAccuracyBest
        locationManager.headingFilter     = 1.0
        locationManager.requestWhenInUseAuthorization()
        locationManager.startUpdatingLocation()
        locationManager.startUpdatingHeading()
        startMotionUpdates()
        startRealTimeTick()
    }

    deinit {
        stop()
    }

    // MARK: - Control

    func stop() {
        motionManager.stopDeviceMotionUpdates()
        locationManager.stopUpdatingLocation()
        locationManager.stopUpdatingHeading()
        updateTimer?.invalidate()
        updateTimer = nil
    }

    // MARK: - World-Space Transform

    /// Converts a solar `SunPosition` into a SceneKit world-space position on a sphere of given `radius`.
    /// Orientation is relative to ARWorldTrackingConfiguration(.gravityAndHeading), so north = -Z axis.
    func worldPosition(for sun: SunPosition, radius: Float) -> SCNVector3 {
        let elev = Float(sun.elevation.radians)
        let az   = Float(sun.azimuth.radians)          // clockwise from north
        let x    =  radius * cos(elev) * sin(az)
        let y    =  radius * sin(elev)
        let z    = -radius * cos(elev) * cos(az)       // -Z = north in ARKit gravity+heading
        return SCNVector3(x, y, z)
    }

    // MARK: - Private helpers

    private func startMotionUpdates() {
        guard motionManager.isDeviceMotionAvailable else { return }
        motionManager.deviceMotionUpdateInterval = 0.05
        motionManager.startDeviceMotionUpdates()
    }

    private func startRealTimeTick() {
        updateTimer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { [weak self] _ in
            guard let self, let coord = self.coordinate else { return }
            self.currentPosition = SunMath.calculateSunPosition(date: Date(), coordinate: coord)
        }
    }

    private func refreshArc() {
        guard let coord = coordinate else { return }
        arc          = SunMath.sunPathArc(for: Date(), coordinate: coord)
        riseSet      = SunMath.sunRiseSet(for: Date(), coordinate: coord)
        currentPosition = SunMath.calculateSunPosition(date: Date(), coordinate: coord)
        isReady      = true
    }

    // MARK: - CLLocationManagerDelegate

    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard coordinate == nil, let loc = locations.last else { return }
        coordinate = loc.coordinate
        refreshArc()
    }

    func locationManager(_ manager: CLLocationManager, didUpdateHeading newHeading: CLHeading) {
        heading = newHeading.trueHeading > 0 ? newHeading.trueHeading : newHeading.magneticHeading
        if coordinate != nil { isReady = true }
    }

    func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
        print("[Sunseeker] Location error: \(error.localizedDescription)")
    }

    func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
        switch manager.authorizationStatus {
        case .denied, .restricted:
            locationError = "Location access needed to calculate the sun path. Please enable it in Settings."
        case .notDetermined:
            manager.requestWhenInUseAuthorization()
        default:
            locationError = nil
        }
    }
}

// MARK: - Degree helpers (internal to this file)

private extension Double {
    var radians: Double { self * .pi / 180.0 }
}